1. Field of the Invention
This invention relates to a multistage hydraulic machine for a pumped-storage or a hydro-electric power plant, and more particularly to a multistate pump, turbine or pump-turbine including an outer backchamber, an inner backchamber and a sidechamber around the runners of each stage, and forming complicated water passages.
2. Description of the Prior Art
It is now explained that a prior art two-stage hydraulic machine is shown in FIG. 1 as one example of the hydraulic machine. In FIG. 1 a numeral 1 represents a runner of a lowpressure-stage, a numeral 2 represents guide vanes of the lowpressure-stage, a numeral 3 represents a runner of a highpressure-stage and a numeral 4 represents guide vanes of the highpressure-stage. The lowpressure-stage is coupled in series to the highpressure-stage through a return pipe 5. Moreover, for the highpressure-stage a casing 7 is provided to the periphery of the guide vanes 4, and for the lowpressure-stage a draft tube 6 is provided to the outlet side on the water-turbine operation. Furthermore, a turbine generator (not shown), which acts as a generator on the water-turbine operation and acts as a motor on the pump-turbine operation, is coupled to a shaft. In a main passage explained above, the chamber around the runners, which takes part in causing an axial water thrust, comprises an outer backchamber 8a, an inner backchamber 9a, a side backchamber 10a and a runner outlet portion 11a in the lowpressure-stage, and an outer backchamber 8b, inner backchamber 9b, a sidechamber 10b and a runner outlet portion 11b in the highpressure-stage.
In the hydraulic machine of a multistage pump-turbine having the passage explained above, the axial water thrust which acts on the runner 1 of the lowpressure-stage is given by multiplying the area and water pressure in each chamber of pressure described above, i.e. by summing each hydraulic load in each chamber of pressure as in following equation 1. EQU T.sub.1 =Ta.sub.1 +Tb.sub.2 -Tc.sub.1 -Td.sub.1 -Tr.sub.1 ( 1)
Where,
T.sub.1 : axial water thrust PA1 Ta.sub.1 : hydraulic load in the outer backchamber 8a PA1 Tb.sub.1 : hydraulic load in inner backchamber 9a PA1 Tc.sub.1 : hydraulic load in the sidechamber 10a PA1 Td.sub.1 : hydraulic load in the runner outlet portion 11a PA1 Tr.sub.1 : reaction force caused by a water flow in the runner
(the load normally acts downward in FIG. 1) PA2 (the load normally acts downward in FIG. 1) PA2 (the load normally acts upward in FIG. 1) PA2 (the load normally acts upward in FIG. 1) PA2 (the reaction force normally acts upward in FIG. 1)
On the other hand, the axial water thrust, which acts on the runner 3 in the highpressure-stage, is similarly found by substituting from the suffix 1 to the suffix 2 in above-mentioned equation 1. EQU T.sub.2 =Ta.sub.2 +Tb.sub.2 -Tc.sub.2 -Td.sub.2 -Tr.sub.2 ( 2)
The axial water thrust T as resultant of all stages is given by summing the above axial water thrusts of the lowpressure-stage and highpressure-stage as in following equation 3. EQU T=T.sub.1 +T.sub.2 ( 3)
The water thrust T described above normally acts in the direction from the highpressure-stage to the lowpressure-stage, i.e. downward in FIG. 1 so as to thrust a rotational part of the hydraulic machine. Since an excessive water thrust T often brings on such accidents as damaging the thrust bearing of the generator or the motor directly coupled to the runner, it is a most important problem in the operation control to control the stability of the water thrust T, especially in a hydraulic machine including a runner on each stage and forming a complicated passage.
Under such circumstances, it is the situation that the multistage hydraulic machine having a reliable and adequate controlling means for the water thrust T is still not available since the multistage hydraulic machine per se is unperfected.